What’s the best way to measure the depth of a well using a smartphone? If you’re fed up with social media, you might kill two birds with one stone and drop the thing down the well and listen for the splash. But if you’re looking for a less intrusive — not to mention less expensive — method, you could also use your phone to get the depth acoustically.
This is a quick hack that [Practical Engineering Solutions] came up with to measure the distance to the surface of the water in a residential well, which we were skeptical would work with any precision due to its deceptive simplicity. All you need to do is start a sound recorder app and place the phone on the well cover. A few taps on the casing of the well with a hammer send sound impulses down the well; the reflections from the water show up in the recording, which can be analyzed in Audacity or some similar sound editing program. From there it’s easy to measure how long it took for the echo to return and calculate the distance to the water. In the video below, he was able to get within 3% of the physically measured depth — pretty impressive.
Of course, a few caveats apply. It’s important to use a dead-blow hammer to avoid ringing the steel well casing, which would muddle the return signal. You also might want to physically couple the phone to the well cap so it doesn’t bounce around too much; in the video it’s suggested a few bags filled with sand as ballast could be used to keep the phone in place. You also might get unwanted reflections from down-hole equipment such as the drop pipe or wires leading to the submersible pump.
Sources of error aside, this is a clever idea for a quick measurement that has the benefit of not needing to open the well. It’s also another clever use of Audacity to use sound to see the world around us in a different way.
slightly related: I used audacity to measure the switching time of a on/on switch by shorting (ok, with current limiting resistor) the mic-in with both switch-contacts parallel, which gave a relatively nice and reasonably repeatable rectangle signal with a width of about 2 ms for every flick
Used to record the sound of a passing object (e.g., an RC plane) and then estimate its speed using Audacity to measure the doppler shift. Now there are apps for that.
Hehe. I taught my teacher how to measure the speed of passing cars that way with only his ears. He was a good musician and had an uncannily accurate pitch estimator built-in. He could judge the pitch shift, and just needed a way to convert that into speed. He was my math teacher, so I suspect the exercise was mostly for my benefit, but he seemed genuinely appreciative when I showed him how to convert centitones to miles per hour.
If it has magnets you can get an exact signal using a loop of wire connected to the microphone jack. Some protective diodes may be needed.
I use an app called Phyphox that has a built in sonar. It also has tons of other useful tools using sensors that most smartphones have.
I definitely recommend checking it out.
Thank you!
@Dan Maloney
This app is really worth being checked out – it’s not just any app, but has a lot of features and interface possibilities. You could add it to the article, or even it’s own article.
It’s supported by the famous University RWTH Aachen!
Used Phyphox to distinguish between two possible causes of an engine noise (failed valve lifter or slap caused by a failed piston skirt). The latter would have been VERY expensive. At idle (~600 rpm or 10 cycles/second) the valve lifter on a 4 stroke engine would be 1/2 engine speed (5 Hz) while the piston slap would be at 10 Hz. That spike at ~5 Hz was a (relatively) happy sign.
Thanks for the app info, I just installed it and wow is it loaded with tools. Awesome! Thanks again and again!
Funny story: A guy I used to work with had a family business that made wood dipsticks to measure fuel depth in buried tanks — you know, the ones at pretty much every gas station.
He was a trained electronics technologist and figured he’d reinvent the business and make a killing by making an “acoustic dipstick”: a cap for the tank that just pinged the surface of the fuel and measured the distance, making a readout in the office. No trudging out to the tank to make a measurement, no replacing broken dipsticks. Should be a slam dunk, right? Especially with the customer rolodex already in hand.
After going through all the explosive atmosphere intrinsically-safe stuff he had a working product, but couldn’t sell any. Nobody would trust it. Because a wood dipstick can’t lie.
Now you see them all the time as stream height gauges, suspended under bridges. And his company still makes wood dipsticks.
I’m kind of surprised the acoustic ones didn’t sell. It sounds pretty annoying to do by hand considering that there’s probably lots of gas fumes involved and then you have a probably dripping dipstick full of gas to deal with.
The company pays a kid to dip the tanks. They get accurate numbers, and the kid won’t develop the resulting health problems until years after he/she left the job. Company saves a fortune, kid can’t figure out how they got lung cancer when they never smoked.
Yes, that ten second exposure a few days a week is going to cause a lot of harm. Not.
plus the hypothetical kid gets way more exposure to gasoline fumes (and other fun things) just from working at the gas station.
I think people are overestimating how much of a chore/risk it is to poke a stick in a hole occasionally, even if that hole is full of nasty, soggy hydrocarbons.
Also the dipstick can get a special paint that will change colour in the presence of water in the bottom of the tank. So you can measure the condensate and the fuel on the same scale. I bet water on your dipstick means other things too, but im not a tank whisperer.
There’s a paste called ColorCut that has been used for decades to find the water contact point in crude oil. It changes from yellow to red when it contacts water. It can be used on a still line or a wooden stick.
Long time reader, first time commentary: there is an open source android app called phyphox that has an acoustic distance measurement tool that is actually really accurate!
Time domain reflectometry in acoustic form.
Also known as sonar!
This is not a simple “divide by 2” problem. You need to form a quadratic equation to solve this. By the time you’ve heard the sound, the object has ALREADY hit the bottom before this. First, calculate how long the object would take to hit the bottom, then calculate how long sound would take to reach the top; this is now the total time. Solve this and you’ll remove the 3% error.
There is no object hitting the bottom… He’s reflecting sound waves that originate from the top…
You should probably reread the article.
Wasn’t this origins of current day audio “auto tune” and also oil finding methods below the ocean floor?
Temperature : sound speed is dependant of temperature, and well temp is a vertical gradiant rather difficult to estimate.
You can estimate it well enough as the average of the well water temperature and near-surface ground temperature. The change in the speed of sound in air changes less than 3% from 10 to 25 Ā°C. Humidity also affects things a bit. I’ve used a similar method on a 39 m well and got a result within .2 m of the direct measurement.
In my case I used my phone to emit a chirp to measure the echo of. I used 10 kHz successfully, but from what I saw on the recorded audio, 1 kHz might have been a better choice.
Just throw a stone in the water and measure the free fall time. Even better, if you’ve thrown enough stones the water comes to the top and you don’t need a pump anymore.
Uh, that’s not how wells work…
Clearly you don’t know what an actual well looks like.
Used to use similar to measure the depth of fluid in oil wells. Used a black powder blank for sound and a disc plotter to measure the time.
Thanks for the article. In industrial seismology we deduce what the structures are under the ground by using sound waves. The sound waves reflect and refract from the underlying layers of material as these have different densities. My first job in the mid 90s found me hitting a metal plate with a sledge hammer in the middle of a swamp in Nigeria to generate the sound waves. The reflections and refractions were detected by a short string of geophones. The data was recorded to a floppy which we interpreted at base camp. This was to figure out how thick the layer of mud and soil was over the ground rock. The main survey used dynamite as a source and strings of geophones some kilometers long to detect the signals.
Floppy disk?
Luxury!
(1987 JAFO in the Middle East)
This reminds me of a story that was in a letter to Scientific American back in the 1970s concerning one of the expensive mechanical watches by, I think, Rolex, that had a depth function built in. It described an insufferable owner who would take every opportunity to demonstrate this functionality by holding their watch in one hand and a rock in the other, and as they dropped the rock they pressed the magic button to start the timer, pressing again to stop when the sound of the rock was heard reading the depth on the handy scale. This continued right up until he dropped the watch and clicked the rock…
Most domestic wells around here are PVC cased, not to mention having a steel plate sanitary well seal deterring access. We own a sonic sounder, but its accuracy is limited when there is not an unobstructed shot to the surface of the water. Have your contractor run an airline down the the pump next time it is out. We do it on all of our installations. With a pressure gauge, compressed air, a little math and a few other odds and ends, anyone can accurately and non-intrusively measure the water level in their well.
With the airline in place you can hack a cheap (or discarded) blood pressure monitor to check the fluid level. You get the distance between fluid surface and lower airline end as long as it is submerged. If the monitor is old enough it doesn’t even need electricity (bt, dt, got Passierschein A38)
A blood pressure monitor will max out at 6 to 8 feet of water depth, and probably get destroyed at 50 feet.
The last house I lived in had a 220 foot deep well, routinely with more than 150 feet of standing water in it.
Then get the airline end to the level you consider “empty”, and you can read the lowest 10 ft at linear scale and all above that as “full”. I used it on a rain water cistern about 1,5 m (~5 ft) deep, worked fine; how much variability is usual on ground water levels?
You can also investigate if you can determine the resonant frequency of the column via a sweep. Just remember to factor in air pressure and temperature of the air in the column if you want high accuracy.
EchoMeter in oil and gas industry has been there for nearly 20 years, they shoot impulse wave with a CO2 cartridge, very simple, reliability depends on many things, well completion being the biggest, but quite useful for shallow formations with static/flowing levels above the deviation curves into horizontal production liners.